Apparatus and method for manufacturing products from a thermoplastic mass

ABSTRACT

An apparatus for manufacturing products from material which is thermoplastically deformable, as from plastic, comprising:—a mold ( 2 ) with at least one mold cavity ( 3 );—in the or each mold cavity ( 3 ) at least one slide ( 8 );—movement means for moving each slide ( 8 );—closing means for opening and closing the mold ( 2 );—feed means for introducing, with the mold cavity ( 3 ) closed, said material in at least substantially plastic condition into the or each mold cavity; wherein the movement means ( 9 ) for moving the slide ( 3 ) are arranged for moving said slide forward at a relatively high speed relative to the movement speed of the mold parts upon opening and closing thereof, from a position at least partly retracted from the mold cavity, such that said material, as a result, is displaced in the mold cavity for obtaining the filling thereof, preferably at a speed high such that adiabatic heat development occurs in the or each mold cavity.

This application is the U.S. National Phase of International ApplicationNumber PCT/NL2003/000630 filed on 10 Sep. 2003, which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

The invention relates to an apparatus for manufacturing products from anat least thermoplastically deformable material. Such a method is known,for instance, as injection molding.

With known injection molding techniques, as a rule, the material to beformed such as plastic is heated in a plasticizing device to atemperature such that the material becomes virtually liquid, at leastplastic and low-viscous, whereupon the material is introduced under highpressure into a mold cavity of an injection molding mold. In this moldcavity, the material is distributed such that the mold cavity iscompletely filled, whereupon the material is allowed to cure by coolingdown. Thereupon, the product is taken out by opening the mold andejecting the product.

For such known injection molding techniques, a particularly high feedpressure is to be used, especially when thin-walled products are formed,in particular if the flow paths in the mold cavity closely approach themelt flow index (MFI) of the materials to be used. Therefore, the sameholds in particular when the flow paths in the mold cavity arerelatively long. It is clear that with plastics with a high viscosityand/or a low melt flow, these problems occur to a larger extent. As aresult, limitations are imposed on the minimum and maximum sizes ofproducts, in particular on lengths of flow paths, on passage widths ofsuch flow paths, on the duration of the injection molding cycles, on thematerials to be used and on the minimum wall thicknesses of products, inparticular of large, flat parts.

The use of compression molding is already known. Here, into a moldcavity of a partly open mold, an amount of plastic is introduced,required for forming a desired product in this mold cavity. After theplastic has been introduced into the mold cavity, the mold is closedfurther, so that the plastic is pushed away for filling the further moldcavity. Therefore, with such an apparatus, at the start of theintroduction of the plastic, the mold parts are to be held partly awayfrom each other, and only afterwards to be brought onto each otherrelatively slowly but with high pressure. The danger exits that then,the plastic is not uniformly distributed, so that, for instance, a partof the material can be pressed sideways from the mold cavity before themold cavity is completely closed. Also, the danger exists thatinsufficient or, conversely, too much plastic is introduced into themold cavity. In this latter case, skin formation will occur between themold halves and, moreover, it will not be possible to close the moldcompletely. This leads to irregularly formed products and, moreover, topollution of the mold. A further disadvantage of this apparatus is thatwhen materials are used with a low viscosity and/or with shallow moldhalves, the material flows from the mold cavity before the mold halvesare moved together, so that the earlier mentioned problems occur to aneven larger extent.

The object of the invention is to provide an apparatus of the typedescribed in the opening paragraph, wherein in a simple manner and withrelatively low closing pressures, products can be manufactured having atleast parts with a relatively limited wall thickness.

A further object of the invention is to provide a apparatus of the typedescribed in the opening paragraph, wherein different materials can beprocessed, in particular plastics, in particular also plastics with ahigh melt, i.e. plastics with a low viscosity in plastic state.

A still further object of the invention is to provide a method withwhich, in a relatively rapid and simple manner, products can bemanufactured, with relatively simple means, which products, moreover,can have relatively large, thin-walled surfaces, in particular productswith wall thicknesses which are relatively small and flow paths whichare relatively long, smaller or longer, respectively, than matching themelt flow index associated with the material from which the product ismanufactured.

The invention further contemplates providing an improved use of aninjection mold with a slide.

A number of these and many other objects are achieved with an apparatus,method and/or use according to the invention.

SUMMARY OF THE INVENTION

An apparatus according to the invention is characterized by the featuresof claim 1.

With an apparatus according to the invention, a thermoplastic materialsuch as a plastic, in particular a thermoplastic plastic, can beintroduced into a mold cavity while the mold as such is closed and theor each slide is in, or is being brought into, a retracted position atintroduction of the material, so that the volume of the mold cavity isrelatively large with respect to the volume of the product to beeventually formed. After the material has been introduced entirely or,preferably, substantially into the mold cavity, the or each slide can bemoved forcefully and, in particular, with speed into the mold cavity, atleast into the material introduced therein, so that this is pushed away.With it, a speed is developed such that, as a result of the movement ofthe or each slide, heat development occurs in the material. To that end,the movement means are designed such that the slide can move at thedesired high speed and with the desired accuracy.

Preferably, the movement means and the slide are designed such thatadiabatic heat development occurs, so that the temperature in thematerial rises above the melting temperature of the respective material.

In an advantageous embodiment, the closing means are included at leastpartly in or on the mold, preferably such that no press is required orthat a press without guide rod can suffice. Optionally, also, blockingmeans can be provided on the mold for holding the mold in closedcondition during introduction of the material and displacement of the oreach slide.

With an apparatus according to the invention, the mold can be heldclosed with relatively little closing pressure and the plastic can beintroduced, in comparison with a conventional injection moldingapparatus. By way of illustration: with conventional injection molding,feed pressures of between, for instance, 350 bars and 1000 bars or moreare used, with closing pressures of, for instance, 0.25 to 1.25 ton/cm²,depending on, in particular, the material used, the wall thickness andthe maximum flow path. With a method according to the invention, forcomparable products, a feed pressure of, for instance, between 0 and 200bars excess pressure can suffice, while relatively low pressures arepreferred, for instance of some tens of bars or less. In the Table, anoperating pressure of approximately 300 bar (operating pressure of thecylinders of the slides) is given, while the closing pressure can be,for instance, less than 0.2 ton/cm². With polypropylene, for instance, aclosing pressure of 0.025 to 0.1 ton/cm² instead of between 0.25 to 1.25ton/cm² can suffice.

Without wishing to be bound to any theory, this appears, in particular,to be the result of the insight that by temporarily increasing thevolume of the mold cavity, at least when introducing the larger part ofthe material such as the plastic into the mold cavity, the relationbetween the length of the flow paths and their passage, substantiallydetermined by the minimum wall thickness of the product to be formed,becomes more favorable, so that the material experiences relativelylittle counter pressure in the mold cavity, while the injection openingor openings are so small that upon movement of the slide or slides, thematerial is not pushed back through this opening or these openings.Moreover, then, the advantage appears to be achieved that due to thehigh speed of the or each slide, as a result of friction, so much heatis introduced into the material that solidification of the material, inparticular against the mold parts and in the flow front thereof, isundone so that the viscosity of the material is reduced again, while theremaining length of the flow paths for this flow front at the start ofthe movement of the or each slide has been considerably reduced relativeto the original length thereof. As a result, the material can bedistributed in the entire mold cavity with less pressure. As the mold isthen closed, in a simple manner, the material is prevented from flowingaway prematurely.

Surprisingly, it has appeared that then, a high feed rate isparticularly advantageous. For instance, a feed rate can be used ofbetween 100 and 2000 mm/s, more in particular of between 500 and 1000mm/s. This rate is selected depending on the solidification rate of theplastic used, while it holds that the more quickly the plasticsolidifies, the higher the feed rate is chosen to be. Moreover, the rateis selected depending on the mold geometry and, in particular, thede-aeration, such that undesired pressure increase in the mold cavity bycompression of air is prevented.

With a mold according to the invention, in the movement means,preferably, wedge-shaped elements are used which, viewed from the moldcavity, are moved behind the or a slide, such that the respective slideis moved as a result of the wedge-shape. In particular, then, for eachslide at least two wedge-shaped elements are used which are pushed inopposite directions behind the slide so that a symmetrical load isobtained. Through the use of such wedge-shaped elements a favorabledistribution of forces is obtained and the slides can be moved over thedesired distance with relatively little force.

In a mold according to the invention, preferably, at least one slide isprovided at the location where the smallest wall thickness is providedin a product and/or at the location where the flow paths have thegreatest length and/or at the location where the flow paths have thegreatest complexity. By retracting the slides in those parts uponinjection of the plastic, at least moving them partly from the moldcavity, additional space is created for allowing the plastic to passexactly at the location where the plastic experiences the mostresistance or at the location where excessive pressures would benecessary for allowing the plastic to pass. This holds in particular atthe location where already some solidification of the plastic occurs.The adiabatic heat introduced later causes the plastic to flow further,while, moreover, the displacement of the slide effects the furthermovement of the plastic. Furthermore, with such a mold, relativelylarge, thin-walled product parts can be obtained with wall thicknessesthat cannot be obtained with conventional injection molding technique.

Slides in a mold according to the invention can have a frontal surfacewhich is relatively large in relation to the projected surface of theproduct. Herein, projected surface is understood to include the surfaceof the product projected on a plane at right angles to the closingdirection of the mold. For instance, the frontal surface of the slidecan be more than 20% of this projected surface. Surfaces of more than50%, for instance of 75%, 85% or 95% or more are possible. With this,the advantage is achieved that in a major part of the mold cavity, thespace for primary flow of the material to be formed is increased, while,eventually, thin-walled products can be manufactured. As a result ofthis as well, the feed pressure and the closing pressure can be kepteven lower.

The invention further relates to a method for forming products,characterized by the features of claim 10.

With such a method, in a rapid and simple manner, plastic products canbe manufactured, while low pressures can be used for injection of theplastic as well as closure of the mold. As low injection pressures canbe used, the advantage can be achieved that no undesired chemical ormechanical changes occur in the plastic, in particular separation in thedifferent monomers or polymers, while the closing pressure can be keptlow, which is advantageous from a point of view of costs. The fact isthat for that purpose, simpler apparatuses are suitable, while moreover,the mechanical load is lower and less wear will occur. A furtheradvantage thereof is that, in principle, less space is required for suchan apparatus.

With a method according to the invention, plastic is introduced into themold cavity while the or each slide is retracted therefrom at leastpartly or is pushed back upon injection, so that additional flow spaceis obtained. This has already been discussed hereinabove with referenceto an apparatus according to the invention. Thus, the resistance theplastic experiences is reduced, so that the injection pressure can bekept low, for instance largely below the standard injection pressure forconventional injection molding of a similar type of product from thesame plastic. Such standard pressures can be read from standard tablesand, as a rule, are dependent on the plastic and the manner ofinjection, the projected surface of the products to be formed jointlyand the wall thicknesses. As a result thereof, the closing pressure canalso be kept low in relation to conventional injection molding, readablefrom the same or comparable tables on the basis of substantially thesame quantities. This is directly clear to the skilled person.

With a method according to the invention, after the mold cavity has beenat least substantially filled, the or each slide is moved rapidly intothe mold cavity, such that the eventual product shape is obtained. Thespeed of the or each slide is then set such that adiabatic heatdevelopment occurs in the plastic, so that the temperature is increasedagain to approximately the melting temperature of the plastic. As aresult, partially solidified material will become liquid again and bepushed further into the mold cavity, while, furthermore, the remainingflow paths are relatively short so that relatively thin product partscan be formed.

With a method according to the invention, the rate of movement of the oreach slide is preferably high, such that the complete movement of theslides is carried out in a fraction of the cycle time of a productcycle, for instance in less than 10%, more in particular in less than 3%of the cycle time, preferably less than some tenths or hundredths ofseconds, more in particular microseconds. As stated, this rate is setsuch that the desired temperature increase occurs, while the plasticproperties are prevented from being adversely thermally influenced.

With a method according to the invention, the distance between the endof the or each slide, leading in the direction of movement and facingthe mold cavity in the retracted position, at least partly moved fromthe mold cavity, and an oppositely located wall part of the mold cavityor slide is set depending on at least the melt of the plastic, i.e. theviscosity of the plastic upon injection. Surprisingly, it has appearedthat, preferably, at a higher melt, i.e. a higher viscosity, thedistance is to be slightly greater than with a lower melt. Withoutwishing to be bound to any theory, this appears to be the result of thefact that the plastic with the higher melt will solidify sooner and theplastic with the lower melt has a more disadvantageous MFI. For anyplastic/mold combination, the optimal distance can be determined in asimple manner by way of experiments.

The invention further relates to a use of a mold for forming products,characterized by the features of claim 19 and a product, characterizedby the features of claim 20.

BRIEF DESCRIPTION OF THE DRAWINGS

In the subclaims, further advantageous embodiments of the invention aredescribed. In clarification of the invention, exemplary embodiments ofan apparatus, method, use and product will be described with referenceto the drawing. In the drawing:

FIG. 1 shows, in partly cross-sectional side view, an apparatusaccording to the invention, with partly opened mold;

FIG. 2 shows, in partly cross-sectional side view, an apparatusaccording to the invention, with a closed mold and retracted slide;

FIG. 3 shows, in partly cross-sectional side view, an apparatusaccording to the invention, with a closed mold and forwardly movedslide;

FIG. 4 shows, in partly cross-sectional side view, an alternativeembodiment of an apparatus according to the invention;

FIG. 5 is a graph showing the temperature in the plastic in a moldaccording to the invention during an injection molding cycle, plottedagainst time; and

FIG. 6 shows a depiction of a CD-box manufactured according to theinvention, photographically recorded using colorant.

In this description, identical or corresponding parts have identical orcorresponding reference numerals. The embodiments shown are only givenby way of example and should not be taken as being limitative in anyway.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows, in cross-sectional side view, an apparatus 1 according tothe invention, provided with a mold 2 with a mold cavity 3 therein. Themold comprises a first, moveable part 4 and a second, complementary part5, fixedly arranged. The moveable part 4 is guided by suitable guides,which are not shown but can, for instance, be sliding pins, rails, guiderods or a press or the like and which are directly clear to the skilledperson. The moveable part is moveable with the aid of devices suitableto that end, represented in FIGS. 1-3 as piston-cylinder assemblies 7.It is clear that this may be any suitable device, for instance also asimple press, screw means such as spindles as shown in FIG. 4, linksystems or the like. These can be of relatively light design as they areonly meant for moving the part 5, virtually not for absorbing tensile orpressure forces in the further cycle.

In the fixed part 5, a slide 8 is provided, moveable in the direction Sbetween a retracted position shown in FIGS. 1 and 2, and an extendedposition shown in FIG. 3. For moving the slide 8, two wedges 9 areprovided, to be called wedge-shaped elements, which are moveable in adirection P with the aid of piston-cylinder assemblies 10 which are, forinstance, hydraulically driven from a central control unit 11. Thewedges 9 move in the direction P approximately at right angles to thedirection S. At the underside, the slide 8 is provided with two surfaces12 inclining in opposite directions, complementary to the top surfacesof the wedges 9, such that if the wedges 9 are moved inwards, towardseach other, the slide 8 is moved upwards (directions viewed in the planeof the drawing) towards the extended position and vice versa.

An inflow opening 14 terminates in the mold cavity 3 and is connected toan injection device 15, for instance a plasticizing device and,optionally, a pressing device. On both parts 4, 5 of the mold 2, flanges16 are provided which, with the aid of blocking means 17, can be pressedand held onto each other, for keeping the mold closed. To that end, inthe embodiment shown, the blocking means comprise brackets 18 which aremoveable with the aid of piston-cylinder assemblies 19 and can be pushedover the flanges 16. In this way, simply, the desired closing pressurecan be obtained and maintained.

As an example, on the top surface 20 of the slide 8, two ribs 21 areprovided extending over the entire width of the slide 8, at right anglesto the plane of drawing. The distance D between the end 22 of the ribsleading in the direction of movement, and the oppositely located surface23 of the mold cavity is set with the slide 8 retracted, depending onthe desired product wall thickness and the plastic to be used, while thedistance is set to be larger according as the melt of the plastic ishigher and/or the melting temperature of the plastic is lower.

With an apparatus according to FIGS. 1-3, a product can be formed, forinstance a sheet with two hinges from thermoplast such as polypropyleneor polyethylene, as follows.

The mold 2 is closed from the position shown in FIG. 1, as shown in FIG.2. The distance D is then set at a suitable value, such that the spacein the mold cavity 3 is relatively great. Through the inflow opening 14,under relatively low pressure, plastic is introduced into the moldcavity, for instance at a pressure of between 1 and 10 bars excesspressure. The filling pressure is selected such that a desired, shortfeed time is achieved without the material properties of the plasticbeing adversely affected and without undesirably high pressure occurringin the mold cavity. Then, at a relatively high speed, the slide 8 ismoved forward, in the direction of the extended position, a shown inFIG. 3, by moving the wedges 9. Here, the speed is selected dependent onthe desired adiabatic heat development which should be such that thetemperature of the plastic is at least substantially increased toapproximately the melting temperature thereof. Plastic that is,possibly, slightly solidified becomes liquid again and can be forcedfurther into the mold so that a complete filling of the mold cavity isobtained while the product can have wall thicknesses which are, in fact,too small for the melt flow index of the respective plastic/productcombination. Optionally, after removing the slide, some hold pressurecan still be given with the aid of the injection device 15, so thatundesired stresses can be pressed from the product.

After that, the mold can be opened again and the product can be takenout.

Preferably, the rate of movement of the or each slide is high such thatthe time of movement of the slide between the retracted and the extendedposition is relatively short with regard to the cycle time for themanufacture of a product, for instance between 0 and 10% of that time,also depending on the desired adiabatic heating. This can be determinedby way of an experiment for each plastic-product combination or becalculated with the aid of standard tables regarding plastics, theproduct properties such as dimensions and flow paths, the friction whichwill occur when moving the slide and the heat capacity and melttemperature of the plastic.

In FIG. 4, an alternative embodiment of an apparatus according to theinvention is shown, wherein screw spindles 25 with nut blocks 26 areused for opening and closing the mold 2. These can be wholly or partlyincluded in the mold 2. In this embodiment, the plastic is introducedvia a side inflow opening 14 and a slide 8 is provided on both sides ofthe mold cavity 3. In this embodiment, they can be moved independentlyof each other but it is preferred that they be moved in coupledrelation, so that a symmetrical load occurs in the mold 2.

By way of illustration, an embodiment of a mold and method according tothe invention will be described. As a product example, a plastic file istaken. In Table 1, the data of the injection molding machine areincluded, in Table 2 the mold data, in Table 3 the product dimensions,in Table 4 the data about the slides or pressure plate and in Table 5data involving the operation parameters. In Table 6, the pressures andspeeds used during a injection molding cycle are given. Thereupon, inFIG. 5, the temperature in the plastic in a mold according to theinvention during an injection molding cycle is given, plotted againsttime.

TABLE 1 Machine data Machine Stork SX 3000-2150 Machine number X 2936Year of construction 2000 Main feed 400 V 50 Hz Main current 354 AControl voltage 24V Max Oil pressure 210 bar Max Air pressure 8 barWeight closing force 8700 kg Weight Injection force 5000 kg Screwdiameter 65 mm

TABLE 2 Mold data Length 1050 mm Width 455 mm Height 495 mm Number ofcavities 1

TABLE 3 Product size Length 655 mm Width 320 mm Thickness 1.7 mm

TABLE 4 Pressure plate data Cylinder stroke 50 mm Cylinder diameter 80mm Operating pressure 300 bar Wedge angle 4°

TABLE 5 Parameters Mold temperature 50° Temperature at introduction 245°Dosing 128 mm Shot weight 295 gram Impact of the pressure plate 80 mmDecompression 10 mm Closing force 150 ton Hold pressure 25 bar Thrust 20bar Speed of impact 0.4 S

TABLE 6 Cycle time Sub time At time Total time Closing 0.750 S T = 0.000S 0.750 S Injection 0.171 S 0.750 S 0.921 S Impact 0.400 S 0.857 S 1.257S pressure plate Cooling 12.000 S  1.257 S 13.257 S  Opening 1.000 S13.257 S 14.257 S  Handling 5.000 S 14.257 S 19.257 S 

With a method according to the invention, at a time 0, with the moldclosed, an amount of plastic was introduced into the mold cavity,sufficient for manufacturing an end product, in this case a file. In0.1706 sec, a shot weight of 128 grams of PP was introduced into themold cavity. The mold cavity comprised a slide with a frontal surface ofapproximately 200,000 mm², which was moved over a distance of 1.8 mm.The plastic was introduced, at a temperature of approximately 245° C. ata speed of 750 mm/s, without pressure, at a mold temperature ofapproximately 50° C., and was cooled down in a first phase toapproximately 230° C. At the time T1, after approximately 0.107 seconds,the slide was set in motion, which slide was moved completely forwardsin approximately 0.4 sec, while the temperature in the mold rose to justbelow the temperature at which the plastic will decompose. From the timeT2, at which the slide was completely moved forward and was held in thatposition, the plastic was allowed to cool down to a temperature wellbelow the melting temperature, close to room temperature, for instance45 to 55° C. This cooling down was done in approximately 12 seconds.Apart from two living hinges, the product thickness on the covers andthe back was on average 1.7 mm by, viewed in frontal surface, 655 mm by320 mm. During cooling down, the application of hold pressure was notnecessary, as a result of the fact that no shrinkage needed to beabsorbed. The product appears to be free of stress, so that a highform-stability is obtained.

As a result of the high speed of the slide, kinetic speed is convertedto heat, while, moreover, friction between the plastic and the mold aswell as in the plastic itself and the compression leads to adiabaticheat development. Until approximately the moment T2 the slide iscompletely moved forward, the plastic in the mold is kept in motion and,furthermore, kept above the melting temperature, so that solidificationis prevented and the flow behavior of the plastic is positivelyinfluenced. As a result, a complete filling of the mold cavity isobtained with limited closing force and filling pressure.

The mold was moved with wedges with a wedge angle of approximately 4°.

With a method according to the invention as described herein, the slideis already moved to the extended position while the plastic is beinginjected into the mold cavity. This also contributes to the plasticbeing kept in motion.

In FIG. 6, a photographic depiction is given of a CD-box manufacturedwith a method according to the invention. Here, the flow pattern of theplastic is clearly visible. FIG. 6 is to be explained as follows.

With conventional injections, a tangle of lines would be visible. Withconventional injecting, these lines are caused by plastic being suppliedunder pressure. A very dark, confused pattern becomes visible andindicates the presence of stresses in the material. Conversely, in thispicture, a particularly quiet image presents itself with attractive,long threaded light patterns. A slight hold pressure causes the two darkspots around the points of injection. In itself, this hold pressure isnot necessary but hold pressure can be advantageous for furtherimproving the product, in particular the flatness thereof. The slightlydarker spots near the center are the result of this hold pressure which,clearly, has remained particularly limited.

The invention is not limited in any manner to the embodimentsrepresented in the drawing and the description. Many variations thereonare possible within the framework of the invention as outlined by theclaims. For instance, a mold 2 according to the invention can compriseseveral mold cavities, while the or each mold cavity car be providedwith one or more slides. The slides can be driven in different manners,for instance directly instead of by the wedges, and with the aid ofdifferent means, for instance electrically. Also, the slides can move indifferent directions, for instance approximately at right angles to thedirection of movement of the mold parts, or be pivoted for reducing thespace in the mold cavity.

These and many comparable adaptations are possible within the frameworkof the invention as outlined by the claims.

1. A method for forming a plastic product comprising the steps of: providing a mold having a first mold part, a second mold part and a slide movable within at least one of said first and second mold parts; closing said first and second mold parts wherein a closed mold cavity is formed, said closed mold cavity being defined by said first mold part, said second mold part and said slide, and said slide being movable within said closed mold cavity; injecting a plastic at a first temperature into said mold cavity while said movable slide is in a retracted position, said first temperature being above the melting temperature of said plastic; cooling said plastic to a second temperature by directly contacting said plastic with an internal surface of at least one of said first mold part, said second mold part and said slide, said second temperature being lower than said first temperature and being below the melting temperature of said plastic wherein said plastic becomes at least partially solidified; and reheating said plastic to a third temperature by moving said slide in a forward direction within said mold cavity, wherein said slide is moved at a speed sufficiently great so as to create heat in the plastic such that said third temperature is higher than said second temperature, and is at least about the melting point of said plastic whereby said plastic becomes more liquid.
 2. A method as defined in claim 1, wherein said plastic is injected in said mold cavity at a filling pressure of less than 350 bars.
 3. A method as defined in claim 1, wherein said third temperature is higher than said first temperature.
 4. A method as defined in claim 1, wherein, prior to the injection of the plastic into the mold cavity, the slide is set at a passage distance, determined by the distance between one end, leading in the direction of movement, of the respective slide and an oppositely located wall part of the mold cavity, which distance is set on the basis of the melt of the plastic to be used in the mold cavity.
 5. A method as defined in claim 4, wherein said passage distance is enlarged when using a plastic with a higher melt.
 6. A method as defined in claim 1, wherein the slide is moved at a speed such that the movement of the slide takes place in, at most, approximately 20% of the total cycle time of a manufacturing cycle, determined by the time between the closure of the mold and the extraction of a ready product.
 7. A method as defined in claim 6, wherein said movement of the slide is carried out in less than 3% of the total cycle time.
 8. A method as defined in claim 1, wherein the closing pressure for the mold is smaller than the conventional injection molding apparatuses for the same products of the same material.
 9. A method as defined in claim 1, wherein the feed pressure and speed are such that at least partial solidification of the plastic occurs during introduction of the plastic, while the or each slide is brought into the mold cavity such that therein adiabatic heat development takes place such that the plastic returns to a liquid condition, at least that its viscosity is reduced such that by moving the slide and, optionally, applying hold pressure, the respective mold cavity is completely filled.
 10. A method as defined in claim 9, wherein overflow spaces are provided in the mold cavity, which are filled with the plastic, wherein the parts filled in the overflow spaces are used as engaging elements for extracting a product formed in the respective mold cavity.
 11. A method as defined in claim 1, wherein the plastic does not completely fill the mold cavity during said injection step and the plastic completely fills the mold cavity during said reheating step.
 12. A method as defined in claim 1, wherein said plastic is injected into said mold cavity with an injection device via an inflow opening of said mold cavity, and wherein said method further comprises the step of applying a hold pressure with said injection device to prevent plastic from exiting said inflow opening of said mold cavity during said reheating step. 